Browsing by Subject "DROPLETS"

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  • Krieger, Ulrich K.; Siegrist, Franziska; Marcolli, Claudia; Emanuelsson, Eva U.; Gobel, Freya M.; Bilde, Merete; Marsh, Aleksandra; Reid, Jonathan P.; Huisman, Andrew J.; Riipinen, Ilona; Hyttinen, Noora; Myllys, Nanna; Kurten, Theo; Bannan, Thomas; Percival, Carl J.; Topping, David (2018)
    To predict atmospheric partitioning of organic compounds between gas and aerosol particle phase based on explicit models for gas phase chemistry, saturation vapor pressures of the compounds need to be estimated. Estimation methods based on functional group contributions require training sets of compounds with well-established saturation vapor pressures. However, vapor pressures of semivolatile and low-volatility organic molecules at atmospheric temperatures reported in the literature often differ by several orders of magnitude between measurement techniques. These discrepancies exceed the stated uncertainty of each technique which is generally reported to be smaller than a factor of 2. At present, there is no general reference technique for measuring saturation vapor pressures of atmospherically relevant compounds with low vapor pressures at atmospheric temperatures. To address this problem, we measured vapor pressures with different techniques over a wide temperature range for intercomparison and to establish a reliable training set. We determined saturation vapor pressures for the homologous series of polyethylene glycols (H-(O-CH2-CH2)(n)-OH) for n = 3 to n = 8 ranging in vapor pressure at 298 K from 10(-7) to 5 x 10(-2) Pa and compare them with quantum chemistry calculations. Such a homologous series provides a reference set that covers several orders of magnitude in saturation vapor pressure, allowing a critical assessment of the lower limits of detection of vapor pressures for the different techniques as well as permitting the identification of potential sources of systematic error. Also, internal consistency within the series allows outlying data to be rejected more easily. Most of the measured vapor pressures agreed within the stated uncertainty range. Deviations mostly occurred for vapor pressure values approaching the lower detection limit of a technique. The good agreement between the measurement techniques (some of which are sensitive to the mass accommodation coefficient and some not) suggests that the mass accommodation coefficients of the studied compounds are close to unity. The quantum chemistry calculations were about 1 order of magnitude higher than the measurements. We find that extrapolation of vapor pressures from elevated to atmospheric temperatures is permissible over a range of about 100 K for these compounds, suggesting that measurements should be performed best at temperatures yielding the highest-accuracy data, allowing subsequent extrapolation to atmospheric temperatures.
  • Sathyanarayanan, Gowtham; Haapala, Markus; Sikanen, Tiina (2018)
    This work describes the interfacing of electrowetting-on-dielectric based digital microfluidic (DMF) sample preparation devices with ambient mass spectrometry (MS) via desorption atmospheric pressure photoionization (DAPPI). The DMF droplet manipulation technique was adopted to facilitate drug distribution and metabolism assays in droplet scale, while ambient mass spectrometry (MS) was exploited for the analysis of dried samples directly on the surface of the DMF device. Although ambient MS is well-established for bio- and forensic analyses directly on surfaces, its interfacing with DMF is scarce and requires careful optimization of the surface-sensitive processes, such as sample precipitation and the subsequent desorption/ionization. These technical challenges were addressed and resolved in this study by making use of the high mechanical, thermal, and chemical stability of SU-8. In our assay design, SU-8 served as the dielectric layer for DMF as well as the substrate material for DAPPI-MS. The feasibility of SU-8 based DMF devices for DAPPI-MS was demonstrated in the analysis of selected pharmaceuticals following on-chip liquid-liquid extraction or an enzymatic dealkylation reaction. The lower limits of detection were in the range of 1-10 pmol per droplet (0.25-1.0 mu g/mL) for all pharmaceuticals tested.
  • Dichlberger, Andrea; Schlager, Stefanie; Lappalainen, Jani; Käkelä, Reijo; Hattula, Katarina; Butcher, Sarah J.; Schneider, Wolfgang J.; Kovanen, Petri T. (2011)
  • Vuorinen, Ville; Aarnio, Mia; Alava, Mikko; Alopaeus, Ville; Atanasova, Nina; Auvinen, Mikko; Balasubramanian, Nallannan; Bordbar, Hadi; Erasto, Panu; Grande, Rafael; Hayward, Nick; Hellsten, Antti; Hostikka, Simo; Hokkanen, Jyrki; Kaario, Ossi; Karvinen, Aku; Kivisto, Ilkka; Korhonen, Marko; Kosonen, Risto; Kuusela, Janne; Lestinen, Sami; Laurila, Erkki; Nieminen, Heikki J.; Peltonen, Petteri; Pokki, Juho; Puisto, Antti; Raback, Peter; Salmenjoki, Henri; Sironen, Tarja; Osterberg, Monika (2020)
    We provide research findings on the physics of aerosol and droplet dispersion relevant to the hypothesized aerosol transmission of SARS-CoV-2 during the current pandemic. We utilize physics-based modeling at different levels of complexity, along with previous literature on coronaviruses, to investigate the possibility of airborne transmission. The previous literature, our 0D-3D simulations by various physics-based models, and theoretical calculations, indicate that the typical size range of speech and cough originated droplets (d